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Cleaner production tools in tanzania

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Cleaner production tools in tanzania

  1. 1. CLEANER PRODUCTION: TOOLS FOR CLEANER PROCESSES IN TANZANIA P.P.A.J. VAN SCHIJNDEL AND F.J.J.G. JANSSEN1 Abstract This article focuses on tools for cleaner production processes with emphasis on two Tanzanian industries. First a description of a process and ways to improve it in an economically and environmentally friendly manner are given. Secondly, tools to survey processes are discussed like exergy analysis, pinch analysis and environmental Life Cycle Assessment. Furthermore, some practical results from an environmental audit and exergy analysis in the soap and cement manufacturing industry in Tanzania are summarised. 1 The authors are at the Centre for Environmental Technology (CMT), Faculty of Chemistry and Chemical Engineering, Eindhoven University of Technology, STO 3.25, P.O.Box 513, 5600 MB, Eindhoven, The Netherlands, Email: p.p.a.j.v.Schijndel@tue.nl, respectively f.j.j.g.Janssen@kema.nl 1. INTRODUCTION The World is in a continuous state of change. There is an increase in global economy and world population, which may endanger earth as an ecosystem. The answer against this threat is called sustainable development. There are several definitions of sustainable development, which are abstract and can be interpreted differently. Commonly used definitions include the one given by the World Commission on Environment and Development (WCED, 1987) in the Brundtland report: ‘Humanity has the ability to make development sustainable - to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs. The concept of sustainable development does imply limits - not absolute limits but limitations imposed by the present state of technology and social organisation of environmental resources and by the ability of the biosphere to absorb the effects of human activities’. In this concept of sustainable development by the WCED, there are three dimensions: environment, development and security. 2. CLEANER PRODUCTION Cleaner production of materials, goods and services is one of the answers for sustainable development. It means production in a way in which resources and energy are used in an efficient way and only small amounts of waste and emissions are produced. Other important factors are the use of renewable resources and the increase in quality of the products. This doesn’t mean that the cleaner production concept is different from that of an economic approach, minimising costs and maximising profits. Because minimising the use of resources and in this way also cutting back on emissions will decrease the costs of a given process. Some other important issues used in this context are source (raw material) reduction, waste reduction and pollution prevention (Allen and Rosselot, 1997). From Table 1, it becomes clear that there are differences between these similar issues. Table 1: Comparison of different issues Change in reactor/process Recycling, in process Waste treatment Cleaner production Yes Yes* - Source reduction Yes No No Waste reduction # Yes* / No Yes Yes Pollution prevention Yes Yes No -) Not applicable #) Reduction of solid and liquid wastes *) Not necessarily Source: Allen and Rosselot (1997) Energy carriers belong to the most important resources for mankind. The production of energy sources can cause many environmental problems like major accidents, water pollution, maritime pollution, land use and siting impact, radiation and radioactivity, solid waste disposal, hazardous air pollution, deterioration of ambient air quality, acid deposition, stratospheric ozone depletion, and global climate change. These problems may be decreased when the
  2. 2. energy efficiency of processes is increased. Thus there is a need for cleaner production processes. 3. CLEANER INDUSTRIAL PROCESSES An industrial process can be simply outlined, as in Figure 1. The process can be seen as a black box. Resources and energy (work) are the inputs and products, wastes, emissions (air, soil, water), excess heat etc. are the outputs of this process. Figure 1. Schematical drawing of an industrial process For the energy input, one may need to add a separate black box, representing the fact that energy carriers are converted into electricity, power or heat before being used in the actual process, as shown in Figure 2. Figure 2. Schematical drawing of an energy production process In both Figures 1 and 2 there are possibilities for in- process recycling. It means some waste products can be separated from the waste stream and used again as resources. For instance waste heat can be used to make steam. Cleaner production for the two Figures means that there should be a decrease of resources used and an increase of useful products. The traditional way to improve processes towards a more sustainable production uses costly waste treatment facilities added-on at the stack or discharge pipe of the manufacturing plant; so called end-of-pipe treatment. Sometimes end-of-pipe treatment is unavoidable. Looking closer at waste reduction in, and not at the end of the process, it becomes clear this is much cheaper and more sustainable than the ordinary separation procedures using filters, scrubbers, settlers etc. (Allen and Rosselot, 1997). Other disadvantages of end-of-pipe treatment are: • It takes resources to remove pollution; • Pollution removal generates residues; • It takes more resources to disperse residues; • Disposal of residues also produces pollution. It thus becomes clear that there must be a focus on the process as a whole and not only at the pipes leaving the process or the plant. Several ways to improve processes into cleaner production processes are (from simple to more difficult): • improve a process by optimisation procedures, like process control; • Use of other resources, of higher quality, with less impurities; • Improve some process units; • Process integration; • Total change towards more sustainable processes. In the next sections, tools for checking the energy efficiency and environmental impact of a process and possible solutions to increase efficiency and decrease environmental impact are discussed. 4. TOOLS There are several tools available to check, for a given process, whether there are possibilities to decrease the environmental impact. For most chemical and physical processes thermodynamics provide a powerful tool, because thermodynamics can forecast the amount of resources and energy used and sometimes emissions Process Useful Energy Resources Product(s) Wastes Materials and Waste Energy Emissions Utility Process Useful Energy Resources WastesMaterials and Waste Energy Emissions Energy conversion
  3. 3. produced within a certain process (Swaan Arons and Kooi, 1993). Two thermodynamically related tools discussed here are exergy analysis and pinch analysis. Another, non-thermodynamic, tool discussed here is environmental Life Cycle Assessment, shortly LCA. Exergy analysis Exergy analysis is much familiar with the enthalpy or energy analysis. The difference is that in exergy analysis entropy is applied, contrary to energy analysis, which only includes enthalpy. An exergy analysis can be performed for a whole plant or for different unit operations. Information about exergy analysis can be found in literature, Szargut et al. (1988) and Kotas (1995). The following definition for exergy is used normally: ‘Exergy is the maximum amount of work that can be obtained from a stream of matter, heat or work as it comes to equilibrium with a reference environment, and is a measure of the potential of a stream to cause change, as a consequence of not being completely stable relative to the reference environment. Exergy is not subject to a conservation law, but it is destroyed due to irreversibility’s during any process.’ A basic example is the possibility of converting mechanical work into heat with 100% efficiency. Heat has a lower exergy, compared with work - exergy is also called quality of energy. Heat can not be converted into work by 100% efficiency, since heat has a lower quality compared with work. Some examples of the difference between energy and exergy are shown in Table 2. From this table hot water and steam with the same enthalpy have different exergy or quality values. Steam has a higher quality than hot water. Fuels like natural gas and gasoline have exergetic values comparable to their net combustion value. Work and electricity have the same exergy as enthalpy. Exergy can be calculated by product of energy and quality. Table 2: Examples of energy and exergy of different matter Material Energy [J] Exergy [J] Quality [-] Water 80°C 100 16 0.16 Steam 1 bar and 120°C 100 24 0.24 Natural Gas 100 99 0.99 Electricity / work 100 100 1.00 The advantage of exergy analysis over an ordinary energy analysis is the fact that an exergy analysis is more accurate and scientifically correct, because: • Exergy analysis provides a better view on the efficiency of a process; • Exergy analysis is very useful to find the unit operation where efficiency improvements are the most suitable or useful. Each process designer or process engineer should perform an exergy analysis to make all exergy losses visible in the process under study. The method is very powerful when comparing improvement solutions in an objective and quantitative manner. Of course the exergy analysis does not give direct answers on how to improve the process but it gives the best clues where to start, namely at the point where the largest exergy losses appear. Exergy analysis is also used in the design phase and during optimisation of processes. It is a very useful tool when used for comparison of different production routes of a specific product. Using the knowledge from exergy analysis it becomes clear that, for instance, a heat exchanger can be optimised by increasing its heat-exchanging surface, because this decreases the temperature difference, ΔT, of the heat-exchanger at the same heat load conditions. At the same time costs will go up with increasing heat exchanging surface. Therefore there will be an economical/exergetical optimum as visualised in Figure 3. Figure 3. Heat exchanger optimisation Pinch Analysis Pinch analysis is designed for the optimisation of Heat Exchanger Networks (HEN) by matching excess of heat and cold streams in a system (Linnhoff and Alanis, 1991). An economical analysis is also included in the optimisation phase. Experiences (Varwijk et al., 1998) show that using pinch analysis energy savings from 20%-40% are possible with pay back periods less than three years. exergy consumption (operational costs) Heat exchanger surface (capital costs) minimum ΔT Larger ΔT Optimum ΔT
  4. 4. The theory behind pinch technology is quite simple. For a process all hot and cold streams are inventoried; cold streams are the streams that need to be heated and hot streams need cooling. Necessary data are temperatures, flows and heat/cooling duty. A diagram is made with the hot composite and the cold composite, with temperature at y-axis and the enthalpy on the x-axis (see Figure 4). The cold and hot composites may be moved horizontally until the two curves are very close together at one point. This point is called the pinch point; the temperature difference ΔT at this pinch is often chosen to be an offset value of about 10°C. When the optimal situation is calculated from the diagram, an improved HEN can be designed. An important rule of thumb for HEN design is not to perform a heat exchange process from above to below the pinch point. Figure 4. Composite curve with pinch point The area between the hot and cold composite temperature represents an exergy loss, which can of course be lowered by decreasing ΔT to a minimal value. It appears that pinch analysis is a good tool to improve a given HEN for certain conditions. But for a given process, exergy analysis is a much more powerful tool as shown in Wall and Gong (1996) and in two articles (Gaggioli et al., 1991 and Linhoff and Alanis, 1991). In the last two articles pinch and exergy analysis were used to optimise a given process for nitric acid production. Pinch analysis led to a good optimisation, however the optimisation exergy analysis gave a two times higher efficiency than found by pinch analysis. Life Cycle Assessment or LCA The Environmental Life Cycle Assessment is used to improve the environmental impact of products and services but can also be used to improve processes. The LCA of a product studies the environmental aspects and potential impacts throughout a product’s life cycle, (i.e. from cradle-to-grave) from raw material acquisition through production, use and disposal. In contradiction to exergy and pinch analysis, LCA looks at all environmental impacts instead of only problems related to energy use. LCA’s of production processes can be of interest because they are useful for comparison with other production processes in order to distinguish an environmental ranking. Four steps have to be carried out to perform a LCA (Balkema, 1998; Guinée et al., 1993a and b): 1. Goal and scope definition to define the study focus and depth; 2. The inventory analysis; which consists of a thorough mass balance over the production processes; 3. An impact assessment; in which all the emissions and resource uses are translated to environmental effects; 4. Interpretation of the results. Environmental effects used in LCA include ozone layer depletion, greenhouse effect, smog formation, eutrophication, toxic effects for humans and the ecosystem and resource depletion. In this article it is not possible to give an elaborate discussion of all the advantages and disadvantages. Instead of this, a case is presented (Kniel et al., 1996). Case: The Nitric Acid Plant. This example describes the use of LCA for the improvement of a nitric acid plant. In this process NH3 is converted into NO2 which dissolves into water forming HNO3. Because this process is not so efficient, a lot of NOX (NO and NO2) is emitted. There are two effects from this deficiency, high production cost for HNO3 and eutrophication and acidification through the NOX emission. Two solutions presented in the article (Kniel et al., 1996) are (1) end-of-pipe treatment of NOX with ammonia in which N2 and H2O are formed or (2) cleaner production methodology by reaction at a higher pressure to increase the efficiency in which the NO2 is absorbed to form HNO3. Both methods have the same aim, although method (2) is cheaper because it is more efficient in point of view of the product. In method (1) NH3 is used twice in the process, both as reactant for HNO3 and as the end-of- pipe treatment compound. It is also notable that during the production of NH3 one important emission compound is NOX. The amount of acidification and eutrophication for process (2) is lower than for process (1). The conclusion of this case, based on LCA: cleaner production in process is much better than end- of-pipe treatment. T H Pinch ΔTmin Composite hot stream Composite cold stream Qout Qin
  5. 5. Although the usefulness of this tool has been proved, some scepticism on LCA’s carried out will always exist. Without proper data or good set-up of the studies the outcome of the LCA will be of low quality. Other tools Another important tool is the ‘Common Sense’ of the engineer. The process has to be seen as a total not just as a sum of separate processes. Combination of all the tools presented here can provide an even more powerful tool. It is possible to give a summary of some common sense solutions: • Alter the production technique: Use techniques that produce less waste and/or also use less resources. • Alter the resources used; do not use resources which contain material that will be wasted at the end of the process. For instance paints without solvents (powder paints) will not emit solvents during application and curing. Use resources with less waste and less toxic components. • Alter the process management; better maintenance methods, better training for operators. 5. OPTIONS FOR TANZANIAN INDUSTRIES Like is the case for all industries World-wide, there are a lot of opportunities for the Tanzanian industries to improve the quality of production. The efficiencies in use of both resources and energy can increase. There is room as well to decrease effects on the environment, like air, water and noise pollution. The advantages from cleaner production can be very generous; production costs can drop and make room for more possibilities for improving the processes. At the same time security and health conditions at and around the plant will improve. And in almost all cases the increase in process efficiency will decrease emissions to air, water as well as the amount of solid wastes. Ydhego (1993) stresses the fact that there should be put more emphasis on waste reduction and cleaner production rather than on end-of-pipe technologies because of the high costs for these technologies. In order to stimulate cleaner production there must be facilities for training etc. The establishment of the Cleaner Production Centre of Tanzania (CPCT), located at the offices of the Tanzania Industrial Research & Development Organisation, TIRDO, in Dar Es Salaam is one of the first steps to introduce cleaner production in Tanzania. In the past there has also been a first cleaner production programme called CEPITA, cleaner production in Tanzania, the results of which are being audited at this time. Next steps are to educate the engineers and scientist to think in terms of environmental friendly processes, as is intended in the courses at UCLAS (University College of Land & Architectural Studies), and the start of a M.Sc. course in environmental engineering at UDSM (University of Dar es Salaam). A Centre for Environmental Science and Technology at UDSM is planned for beyond the year of 2000. Some examples of cleaner production in Tanzania are listed below. Soap production One of the companies involved in the cleaner production programme of CPCT in 1997 was the ‘Mshindi’ soap factory. Located in an area with a low capacity sewerage system they managed to modify the process into a ‘zero’ waste production plant. The only wastewater they now have comes from sanitary systems, like toilets, showers and kitchen. They are planning to treat this water using a heliophyt filter on site (Van Schijndel, 1997). Other options being carried out are: better truck offloading system to decrease spillage, increased amount of steam pipes in the soap tank to decrease steam use, use of other raw materials, effluent recycling filter to decrease disposable waste and the increase of overall power factor to decrease electricity consumption (CPCT, 1998). Cement production: In 1997 an exergy analysis was performed at the Wazo Hill cement factory at kiln number three to check if such an analysis was possible with scarce data. The analysis proved to be possible. An exergetic efficiency of 37% was calculated for the existing process; there were plenty of possibilities for further improvement to 43% efficiency with pay back times less than 1.5 years (Van Schijndel et al., 1998). Improvement options include improvement of the pre-heater system and installation of a pre-calciner (20% less fuel), improvement of the dust filters (5% less fuel) and better kiln isolation (4% less fuel). Other options are the installation of new burners, isolation of the heat exchangers and preheating of the fuel. Note that an increase in exergetic efficiency decreases the demand for heavy fuel oil and therefore puts less pressure on non-renewable resources. 6. CONCLUSIONS Three tools for cleaner production have been discussed. Pinch analysis can be used in a good way to optimise heat exchanger networks, however exergy analysis appears to be a more powerful tool than pinch
  6. 6. analysis. LCA on processes shows to be a suitable tool when focusing on environmental effects, however there still exists some scepticism about the method. A combination of the tools mentioned, including common engineering sense, may prove to be a much more powerful tool for cleaner production. REFERENCES Allen, D.T and Rosselot, K.S. (1997), “Pollution prevention for chemical processes”, John Wiley& Sons, New York. Balkema, A.J. (1998), “Sustainability criteria for technology comparison”, proceedings of 11th European Junior Scientist Meeting, 12-15 February 1998, Wildpark Eekholt, Germany, pp.1-7. Cleaner Production Centre of Tanzania, CPCT (1998), “Cleaner Production Demonstration Project at Shivji&Sons Limited”, unpublished research report. Gaggioli, R.A., Sama, D.A., Sanhong Qian, El-Sayed, Y.M. (1991), “Integration of a new process into an existing site: A case study in the application of exergy analysis”, Journal of Engineering for Gas Turbines and Power, Vol.113, pp.170-183. Guinée, J.B., Heijungs, R., Udo de Haes, H.A., Huppes, G. (1993), “Quantitative life cycle assessment of products, 1 Goal definition and inventory”, J. Cleaner Production, Vol.1, No.1, pp.3-13. Guinée, J.B., Heijungs, R., Udo de Haes, H.A., Huppes, G. (1993), “Quantitative life cycle assessment of products, 2 classification, valuation and improvement analysis”, J. Cleaner Production, Vol.1, No.1, pp.81-91. Kniel, G.E., Delmarco, K., Petrie, J.G. (1996), “Life Cycle Assessment Applied to Process Design: Environmental and economic analysis and optimization of a nitric acid plant”, Environmental Progress, Vol.15, pp.221-228. Kotas, T.J. (1995), “The Exergy Method of Thermal Plant Analysis”, 2nd edition, Krieger publishing Company, Malabar. Linnhoff, B. and Alanis, F.J. (1991), “Integration of a new process into an existing site: a case study in the application of pinch technology”, Journal of Engineering for Gas Turbines and Power, Vol. 113, pp.159-169. Swaan Arons, J. de, Kooi, H.J. van der (1993), “Exergy Analysis. Adding insight and precision to experience and intuition”, Precision Process Technology, pp.89-113. Szargut, J., Morris, D.R., Stewart, F.R. (1988), “Exergy Analysis of Thermal, Chemical, and Metallurgical Processes”, 1st edition, Springer Verlag, Berlin. Van Schijndel, P.P.A.J. van (1997), unpublished research. Van Schijndel, P.P.A.J. van, Boer, J. den, Janssen, F.J.J.G., Mrema, G.D., Mwaba, M.G. (1998), “Exergy analysis as a tool for energy efficiency improvements in the Tanzanian and Zambian industries”, ICESD Conference Engineering for sustainable development, July 27-29th 1998, University of Dar Es Salaam, Tanzania. Varwijk, J.W.M., Dekker, E. den, Sonderkamp T. (1998), “Pinchtechnologie, effectieve manier van besparen”, NPT Procestechnologie, pp. 36-38 (in Dutch). Wall, G. and Gong, M. (1996), “Exergy Analysis versus Pinch Technology”, Proceedings ECOS’96: “Efficiency, Costs, Optimization, Simulation and Environmental Aspects of Energy Systems”, Stockholm, Sweden. The World Commision on Environment and Development,WCED (1987), “Our Common Future”, Oxford University Press, New York. Yhdego, M. (1993), “Cleaner production in Tanzania”, UNEP Industry and Environment, pp.37- 39.

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